Erythrosine (3′,6′-dihydroxy-2′,4′,5′,7′-tetraiodospiro(isobenzofuran-1(3H),9′-(9H)xanthene)-3-one sodium salt) is a well known dye in pharmaceuticals and alimentary field.
In particular, U.S. Pat. No. 5,620,726 teaches a process for coloring olives characterized in that, before immersing the olives in the erythrosine solution, they are subjected to a bleaching process using sulfurous anhydride or a citric acid solution then, after washing to remove all traces of the said sulfurous anhydride or a citric acid solution, the olives are immersed in a boiling aqueous erythrosine solution, then retrieved, washed to remove all traces of the colorant and packaged.
The sequence of the different steps of the process and the respect of the process parameters and conditions is presented in the patent as essential in order to prevent the finished product having a patchy appearance, that is to say, an uneven color, or to prevent it losing its color after a brief period of time, or during storage or when rubbed, for example, with a cotton pad soaked in water. In particular, before immersing the olives in the erythrosine solution, they are subjected to a bleaching process using sulfurous anhydride or a citric acid solution, this treatment allowing a very pale product to be obtained, ready for the subsequent coloring.
It has been now surprisingly found that a preliminary bleaching treatment is not necessary to avoid a non uniform distribution of the color on their surface, provided particular conditions are met during the dyeing process using erythrosine.